Solid state cell manufacture

Abstract

A unitary polymer electrolyte/polymer-based cathode film component for use in a solid state electrochemical cell is manufactured by solution casting onto one of the electrolyte or cathode, a solution of the other of the electrolyte or cathode. The solution is prepared at elevated temperature (e.g. 40 DEG -50 DEG C.) and cooled to a lower temperature, e.g. ambient, before carrying out the casting. The solvent (e.g. methanol) is such that the polymer (e.g. poly (ethylene oxide)) is only sparingly soluble therein at the lower temperature and relatively readily soluble therein at the elevated temperature. Also, immediate precipitation of the polymer does not occur on cooling the solution from the elevated temperature to the lower temperature. In this way, dissolution of said one of the electrolyte or cathode is avoided.

We claim: 
     
       1. A method of making a solid state electrochemical cell comprising an anode having lithium as its active material, a polymeric electrolyte, and a composite cathode in the form of a composite of an insertion electrode material or similarly active material in combination with a polymeric material, which method comprises the steps of (i) preparing a solution of one of the polymeric electrolyte or the composite cathode material in a solvent at an elevated temperature, the polymer of the electrolyte and the composite cathode and the solvent having the properties that the polymer is readily soluble in said solvent at the elevated temperature, and sparingly soluble in said solvent at a lower temperature, and that immediate precipitation of the polymer does not occur on cooling the solution of the polymer in said solvent from the elevated temperature to the lower temperature;   (ii) cooling the polymer solution to the lower temperature and solution-casting the cooled polymer solution onto a film of the other of the polymeric electrolyte or the composite cathode followed by evaporation of the solvent to form a film of said one of the polymeric electrolyte or the composite cathode thereby to give a unitary electrolyte/cathode film component; and   (iii) assembling said unitary electrolyte/cathode film component with an anode, to form a solid state electrochemical cell.   
     
     
       2. A method as claimed in claim 1 wherein the electrolyte is a complex of a macromolecular material with a lithium salt. 
     
     
       3. A method as claimed in claim 2 wherein the solvent is methanol. 
     
     
       4. A method as claimed in claim 3 wherein the elevated temperature is in the range of 40° to 50° C. and the lower temperature is ambient temperature. 
     
     
       5. A method as claimed in claim 1 wherein the polymer in the electrolyte and cathode material is poly(ethylene oxide).